The invention relates to an axially adjustable steering device for motor vehicles, which comprises two jacket-tube parts of which an outer jacket-tube part is secured to the body and an inner jacket-tube part, in which a steering shaft is fixed axially, is displaceable telescopically in the outer jacket-tube part by means of a controllable drive, a driven worm gear mounted in a reception part engaging into a tooth-profile part extending axially on the displaceable inner jacket-tube part and acting on the latter in a longitudinally displacing manner, a reception part of the worm gear being pivotably mounted fixedly relative to the vehicle and being retained via a locking means in an engagement position of the worm gear and tooth-profile part.
German Patent Specification No. 3,318,935 makes known an axially adjustable steering device for motor vehicles, which comprises two telescopically overlapping jacket-tube parts displaceable relative to one another as a result of the engagement of a driven worm gear into a tooth-profile part on the inner jacket-tube part, in which a steering shaft is fixed axially. The worm gear is mounted in a reception part which is itself mounted pivotably on the outer jacket-tube part fixed relative to the vehicle. To secure an engagement position of the worm gear and tooth profile part, the reception part is retained on the outer jacket-tube part by a locking means, such as, for example, a slot adjustment means.
According to recent findings in vehicle building, the seriousness of the injury to the vehicle driver in the event of a front collision can be reduced if the steering wheel is moved as far as possible away from his body, so that he strikes the steering wheel as late as possible and at only very low speed, if at all.
An object on which the invention is based is, during a front collision, to allow an axially adjustable steering device of the relevant generic type to be displaced into a position shifted furthest in the front direction.
The object is achieved by providing an arrangement wherein the locking means is releasable in a controlled manner during a front collision, and wherein the worm gear is thereafter pivoted out of engagement with the tooth-profile part, with the result that the inner jacket-tube is movable into a position shifted furtherst in the direction of the vehicle front.
In the event of a front collision triggering a control pulse, the lock of the reception part is released automatically and thereby allows the worm gear to pivot away from the tooth-profile part, after which the inner jacket-tube part is no longer supported on a component mounted fixedly relative to the vehicle. The inner jacket-tube part can now be transferred into a position shifted furthest in the direction of the vehicle front, with the result that the vehicle driver can be protected from a rapid impact against the steering wheel.
A favorable design of a locking means releasable in a controlled manner is obtained by means of an electrical separating screw which, in a known way, has a screw portion with an explosion means which, after being ignited by a crash pulse, causes the screw to be severed at a specific separation point. This separation point is located in the region of mutually contiguous surfaces of the outer jacket-tube part and of the reception part locked on it by means of the separating screw, so that after the controlled severance of the separating screw it becomes possible for the worm gear to pivot away from the tooth-profile part immediately.
After this, without further means being required, the steering wheel can move in the front direction either solely as a result of the inertia forces of the displaceable parts or by means of the body forces of the vehicle driver.
For this purpose, the reception part must be arranged pivotably in such a way that it executes the necessary pivoting movement either automatically as a result of its own weight, with the assistance of a spring loading it, or elese as a result of the expulsive force of the tooth-profile part on which force is exerted.
According to advantageous features of preferred embodiments the steering device possesses an element which absorbs energy and which can be formed by a hydraulic damper acting, during the displacement of the jacket-tube parts, with the effect of damping the speed of displacement of the inner jacket-tube in the front direction by counteracting the inertia forces of the displaceable parts after a front collision and, as appropriate, also some of the body forces introduced at the steering wheel. Consequently, even after the worm gear has pivoted away and during the displacement movement of the steering shaft together with the steering wheel in the direction of the vehicle front, the vehicle driver still always has the possibility of support on the steering wheel, with the result that the load exerted by the belt and the maximum value of the relative speed between the vehicle and the vehicle driver can be kept lower.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.